1. Field of the Invention
The present invention relates to a tire vulcanizing apparatus used to vulcanize tires mounted on vehicles such as automobiles and motorcycles. More particularly, it pertains to a tire vulcanizing apparatus capable of vulcanizing a plurality of tires.
1. Description of the Related Art
Tires made of a rubber material are hardened into their final shape by vulcanization. Vulcanization also increases strength and resiliency of the tire. Vulcanization occurs by applying heat and pressure to the tire. Generally, an apparatus for conducting tire vulcanization employs a substantially tubular bladder made of an elastic material such as rubber. The bladder is first inserted inside the tire, which is mounted inside a mold and is then inflated by discharging a heat pressure medium, such as steam, into the bladder. The inflation causes the bladder to press against the inner surface of the tire. The heat and pressure of the medium applied in the bladder forms the tire, pressed against the mold, into its final shape and also vulcanizes the tire.
One type of tire vulcanizing apparatus uses a mold closing apparatus which automatically opens and closes a mold for mounting and dismounting a tire. In such an apparatus, the vulcanizing process includes a vulcanizing step in which the heat pressure medium is discharged into the tire within the mold for vulcanization, and a mount/dismount step in which the tire is mounted to or dismounted from the mold. However, during the vulcanizing process, the vulcanizing step requires much more time than the mount/dismount step. In other words, the closing apparatus remains idle during the vulcanizing step. Hence, the operating efficiency of the closing apparatus is low.
A tire vulcanizing apparatus which improves the operating efficiency of the closing apparatus is disclosed in Japanese Unexamined Patent Publication 7-80845. This apparatus includes a vulcanizing station having a plurality of molds arranged therein, and a mold closing station which opens and closes the molds. A first transporting apparatus is provided to convey the mold between the vulcanizing station and the closing station. A second transporting apparatus is also provided in the closing station to convey the mold between a mold receiving position and a mold closing position. The tire is mounted horizontally inside the mold.
After the vulcanization is completed, the mold is conveyed from the vulcanizing station to the mold receiving position of the closing station by the first transporting apparatus. The mold is then conveyed from the receiving position to the mold closing position by the second transporting apparatus. At this position, a mold closing apparatus opens the mold to dismount the vulcanized tire. Another tire, which is to undergo vulcanization, is then mounted in the mold. Afterwards, the mold is closed by the closing apparatus and sent to the vulcanizing station. The plurality of molds, with the vulcanized tires being conveyed one by one to the closing station, and the plurality of molds with the unvulcanized tires being conveyed one by one to the vulcanizing station, improves the operating efficiency of the mold closing apparatus.
The mold employed in tire vulcanization is generally divided into two sections along a plane perpendicular to an axis of the tire. To dismount the tire from this mold, the mold is opened by relative movement between two mold sections along the tire axis.
However, projections and grooves, which form the tread pattern on the tire, are provided on the inner surface of the mold. When vulcanization is completed, the treads of the tire are engaged with the projections and grooves of the mold. Hence, during removal of the tire from the mold, grooves that constitute the tread pattern are separated from the projections of the mold in a direction perpendicular to the extending direction of the grooves by the relative movement of both mold sections along the tire axis. Therefore, interference between the projections of the mold and the tread occurring during the removal of the tire applies force to the tread portion of the tire. As a result, dismounting of the tire from the mold is difficult. In addition, there is a possibility that a portion of the tire rubber may be damaged during the dismounting.
Therefore, the vulcanizing apparatus disclosed in the above publication employs a mold in which the portion corresponding to the tread portion of the tire is divided into a plurality of sections. Each mold section is moved, or opened, in the radial direction. This construction allows smooth removal of the treads of the tire from the projections of the mold.
However, the tire is mounted horizontally in the above vulcanizing apparatus. Therefore, the vulcanizing station, which has a plurality of molds mounted therein, requires much floor space. In addition, there is a necessity to divide the mold vertically into at least two sections and raise or lower one of the sections from the other. The rigid structure of the mold to withstand the pressure of the heat pressure medium discharged therein, and the mechanism to keep the mold closed when the mold is pressurized by the medium results in a heavy mold. Accordingly, to raise and lower such a heavy mold, a large and rigid elevating mechanism is required. In addition, the vulcanizing apparatus requires high space.
Furthermore, since the first transporting apparatus lifts the heavy mold, the transporting apparatus also is large and rigid. This also increases the required floor space of the vulcanizing apparatus and leads to high equipment costs.
In the conventional vulcanizing apparatus, the portion of the mold corresponding with the treads of the tire is divided into a plurality of sections, arrayed in the circumferential direction, which are opened radially. Therefore, the structure of the mold is complicated and costly.
The mold of the conventional vulcanizing apparatus has a lower bead ring, which supports the lower bead portion of the horizontally mounted tire, and a flange which is raised from or lowered toward the bead ring. The lower rim portion of the bladder is fixed to the lower head ring while the upper rim portion is fixed to the flange. After the unvulcanized tire is mounted inside the mold, discharging of the heat pressure medium into the bladder is started. Simultaneously, the flange is lowered to move the upper rim portion of the bladder to the lower rim portion. Consequently, the bladder presses against the entire inner surface of the tire.
However, With this bladder inserting method, the bladder is not inflated symmetrically about the tire axis. As the bladder is inflated, it applies force against the inset surface of the tire. Therefore, if the bladder is not inflated symmetrically, the force applied to the upper side of the tire and the force applied to the lower side is different. This leads to problems such as different thicknesses between an upper sidewall and lower side wall of the tire.